Method for joining resin and metal

ABSTRACT

A joining method for joining a resin member and a metal member by heating is provided. Joining of the resin member and metal member is performed by heating a joining interface of the resin member and metal member to a temperature in a range of equal to or higher than a decomposition temperature of the resin member and lower than a temperature at which gas bubbles are generated in the resin member and by cooling a surface of the resin member on the opposite side from a joining surface thereof with the metal member to a temperature that is lower than the melting point of the resin member.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a joining method and a joining apparatus forjoining a resin and a metal by heating.

2. Description of the Related Art

Resin members and metal members are usually joined together by using anadhesive, but in order to simplify the joining process and comply withthe Volatile Organic Compounds (VOC) regulations, physical concavitiesand convexities are formed on the joining surface of the metal memberwith the resin member or chemical functional groups are modified byperforming surface treatment such as acid or alkali treatment or aprimer treatment, or a joint body of a resin and a metal is obtained byconducting insert molding of a thermoplastic resin on the joiningsurface of the metal member with the resin member.

In a case where a metal member and a resin member are joined together bya process in which, as mentioned above, the joining surface of the metalmember with the resin member is subjected to a surface treatment,although no adhesive is used, a large amount of surface treatment agentsuch as an acid, an alkali, or a primer treatment agent is used and,therefore, when the spent surface treatment agent is discarded,environmental load is created. In addition, the surface-treated metalmember has to be cleaned and dried, and a long time is required for thecleaning and drying operations. As a result, the aforementioned processis unsuitable for parts that require high productivity, such asautomotive parts or the like. A problem associated with a process inwhich a metal member and a resin member are joined by insert molding athermoplastic resin on the metal member, is that limitations are placedon the shape of the joint body.

Accordingly, for example, Japanese Patent Application Publication No.5-185521 (JP-A-5-185521) describes a method for joining a resin memberand a metal member within a short period by a simple process withoutusing an adhesive or a surface treatment agent and without creatingenvironmental load, wherein the resin member is joined to the metalmember by heating and melting.

In a case where the resin member is heated, as mentioned hereinabove, toa melting temperature or softening temperature, the softened resinmember deforms according to concavities and convexities of the metalmember surface and the two members are joined by the anchor effectdemonstrated due to such deformation, but a sufficient joining strengthcannot be obtained in joining by the anchor effect alone. Furthermore,the resin member is heated by a hot atmosphere inside an oven or with aheater, but if the heating temperature is too high, gas bubbles aregenerated inside the resin and these bubbles cause crack generation inthe resin member after joining. In addition, where the entire resinmember is heated, the resin member is entirely melted and designproperties of the outer surface of the resin member are lost. Theresultant problem is that the application range of the joint of theresin member and metal member is limited.

SUMMARY OF THE INVENTION

The invention provides a joining method and a joining apparatus for aresin and a metal by which a resin member and a metal member are joinedwithin a short period by a simple process, without creatingenvironmental load, a sufficient joining strength can be obtained, anddesign properties of the outer surface of the resin member are notdegraded.

The first aspect of the invention relates to a joining method forjoining a resin and a metal by heating. By this joining method, thejoining of the resin and the metal is performed by heating a joininginterface of the resin and the metal to a temperature in a range ofequal to or higher than a decomposition temperature of the resin andlower than a temperature at which gas bubbles are generated in theresin. With such a joining method, no surface treatment agent is used, anecessary and sufficient joining strength may be obtained within a shorttime, and environmental load in the process of joining the resin andmetal may be reduced. Further, the occurrence of cracks that originatefrom gas bubbles at the joining interface of the resin and metal may beprevented after the joining of the resin and metal, and the joiningstrength of the resin and metal may be ensured.

In the joining method according to the abovementioned aspect, thejoining interface of the resin and metal is heated from a surface of themetal on the opposite side from a joining surface thereof with theresin, and a surface of the resin on the opposite side from a joiningsurface thereof with the metal is cooled to a temperature that is lowerthan a melting point of the resin. With such a joining method, nosurface treatment agent is used, a necessary and sufficient joiningstrength may be obtained within a short time, and environmental load inthe process of joining the resin and metal may be reduced. Further,because the joining of the resin and metal is performed, whilepreventing the resin from thermal deformation during joining of theresin and metal, the design property of the external surface of thejoint body of the resin and metal on the side of the resin is notreduced and the product value of the joint body may be increased.

In the joining method according to the abovementioned aspect, thejoining of the resin and metal is performed by interposing a thin filmhaving an electric resistance higher than that of the metal in theinterface of the resin and metal and high-frequency heating the thinfilm from a surface of the resin on the opposite side from a joiningsurface thereof with the metal. As a result, even when the metal isconstituted by a material with a high thermal conductivity and a lowelectric resistance, the efficiency of heat input to the joining regionof the metal and resin may be increased, the joining interface of themetal and resin may be adequately heated for joining by a simple processand within a short time, and a sufficient joining strength may beobtained.

Further, in the joining method according to the abovementioned aspect, athin film having a laser reflectance lower than that of the metal isinterposed in the interface of the resin and metal, the resin isconstituted by a material that can transmit laser radiation, and thejoining of the resin and metal is performed by emitting laser radiationtoward the thin film from a surface of the resin on the opposite sidefrom a joining surface thereof with the metal and heating the thin film.As a result, even when the metal has a high reflectance of laserradiation, the efficiency of heat input to the joining region of themetal and resin may be increased, the joining interface of the metal andresin may be adequately heated for joining by a simple process andwithin a short time, and a sufficient joining strength may be obtained.

Further, in the joining method according to the abovementioned aspect, aconcavity into which the heated resin can penetrate is formed in a zoneof the metal around a joining region of the resin and metal. As aresult, the softened resin penetrates inside the concavity and an anchoreffect is produced when the metal and resin are joined, thereby makingit possible to increase the joining strength of the metal and resinafter joining.

The second aspect of the invention relates to a joining apparatus thatis used when a resin and a metal are joined by heating. The joiningapparatus includes a heating tool that heats a joining interface of theresin and the metal from a surface of the metal on the opposite sidefrom a joining surface thereof with the resin, and a cooling tool thatcools a surface of the resin on the opposite side from a joining surfacethereof with the metal to a temperature that is lower than a meltingpoint of the resin. With such a configuration, a necessary andsufficient joining strength may be obtained within a short time andenvironmental load in the process of joining the resin and metal may bereduced without using a surface treatment agent. Further, because thejoining of the resin and metal may be performed, while preventing theresin from thermal deformation during joining of the resin and metal,the product value of the joint body may be increased, without reducingthe design property of the external surface of the joint body of theresin and metal on the side of the resin.

Further, in the joining apparatus according to the abovementionedaspect, the heating tool heats the joining interface of the resin andmetal to a temperature in a range of equal to or higher than adecomposition temperature of the resin and lower than a temperature atwhich gas bubbles are generated in the resin. With such configuration,no surface treatment agent is used, a necessary and sufficient joiningstrength may be obtained within a short time, and environmental load inthe process of joining the resin and metal may be reduced. Further, theoccurrence of cracks that originate from gas bubbles at the joininginterface of the resin and metal may be prevented, and the joiningstrength of the resin and metal may be ensured.

In accordance with the invention, no surface treatment agent is used, anecessary and sufficient joining strength may be obtained within a shorttime, and environmental load in the process of joining the resin andmetal may be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further features and advantages of the invention willbecome apparent from the following description of example embodimentswith reference to the accompanying drawings, wherein like numerals areused to represent like elements and wherein:

FIG. 1 is a side view illustrating how a metal member and a resin memberare joined together by using a joining apparatus including a heatingbody and a cooling body;

FIG. 2 illustrates the relationship between the temperature of thejoining surface of the resin member and metal member and the heatingtime;

FIG. 3 is a side view of a joining apparatus in which the heating bodyand cooling body are formed to a shape similar to that of a gun of aspot welding machine;

FIG. 4 is a side view of a joining apparatus in which the heating bodyand cooling body are configured of roller members;

FIG. 5 is a perspective view illustrating the metal member in whichslits are formed on the circumference of the joining region of the metalmember and resin member;

FIG. 6 is a side sectional view illustrating a heat transfer state inthe metal member in which slits are formed on the circumference of thejoining region of the metal member and resin member;

FIG. 7 is a plan view of the metal member in which slits are formed onthe circumference of the joining region of the metal member and resinmember;

FIG. 8 is a side sectional view illustrating a state in which thesoftened resin member penetrated into the slits formed in the metalmember;

FIG. 9 is a perspective view showing a metal member in which a grooveopened at the surface on the opposite side from the joining surface withthe resin member is formed on the circumference of the joining region ofthe metal member and resin member;

FIG. 10 is a side sectional view showing a metal member in which agroove opened at the surface on the opposite side from the joiningsurface with the resin member is formed on the circumference of thejoining region of the metal member and resin member;

FIG. 11 is a side sectional view showing a metal member in which agroove opened at the surface on the opposite side from the joiningsurface with the resin member and a groove opened at the joining surfacewith the resin member are formed on the circumference of the joiningregion of the metal member and resin member;

FIG. 12 is a perspective view showing a metal member in which groovesopened at the joining surface with the resin member are formed on thecircumference of the joining region of the metal member and resinmember;

FIG. 13 is a side sectional view showing a metal member in which groovesopened at the joining surface with the resin member are formed on thecircumference of the joining region of the metal member and resinmember;

FIG. 14 is a side sectional view showing how the joining interface ofthe metal member and resin member is heated using a high-frequencyheating apparatus as a heating body; and

FIG. 15 is a side sectional view showing how the joining interface ofthe metal member and resin member is heated using laser radiation as aheating body.

DETAILED DESCRIPTION OF EMBODIMENTS

An embodiment of the invention will be described below with reference tothe appended drawings.

As shown in FIG. 1, in a joining method of the present embodiment inwhich a resin member 4 and a metal member 3 are joined together, in astate in which the resin member 4 and metal member 3 are stacked, thetwo are joined by heating a joining interface of the resin member 4 andmetal member 3 to a predetermined temperature with a heating body 1,which is a heating tool.

More specifically, for example, the joining interface of the resinmember 4 and metal member 3 is heated by bringing the heating body 1into contact with the surface of the metal member 3 on the opposite sidefrom the joining surface thereof with the resin member 4. Further, theheating with the heating body 1 is conducted so that the joining surface5 of the resin member 4 with the metal member 3 assumes a temperature ina range of equal to or higher than the decomposition temperature of theresin member 4 and lower than a temperature at which gas bubbles aregenerated in the resin member 4.

In this case, as shown in FIG. 2, the decomposition temperature tb ofthe resin member 4 is higher than the melting point ta of the resinmember 4, and the temperature tc at which gas bubbles are generated inthe resin member 4 is higher than the decomposition temperature tb ofthe resin member 4. Further, the temperature td of the heating body 1 ishigher than the temperature tc at which gas bubbles are generated in theresin member 4 (in other words, (temperature td of the heating body1)>(temperature tc at which gas bubbles are generated in the resinmember 4)>(decomposition temperature tb of the resin member 4)>(meltingpoint ta of the resin member 4)). When the resin member 4 and metalmember 3 are joined, the joining of the two is performed by holding thejoining interface of the resin member 4 and metal member 3, strictlyspeaking, the joining surface 5 of the resin member 4, at a temperaturewithin a range of equal to or higher than the decomposition temperatureof the resin member 4 and lower than the temperature at which gasbubbles are generated in the resin member 4 (this range is included inthe hatched portion in FIG. 2), during a predetermined time period ΔT.

At the same time as the heating is performed with the heating body 1 inthe above-described manner, a cooling body 2, which is a cooling tool,is brought into contact with the surface of the resin member 4 on theopposite side from the joining surface 5, and the surface of the resinmember 4 on the opposite side from the joining surface 5 is cooled to atemperature less than the melting point of the resin member 4.

In other words, in a state in which the resin member 4 and metal member3 are stacked, the joining of the resin member 4 and metal member 3 isperformed by heating the joining surface 5 of the resin member 4 that isin contact with the joining interface with the metal member 3 to atemperature in a range of equal to or higher than the decompositiontemperature of the resin member 4 and lower than the temperature atwhich gas bubbles are generated in the resin member 4 and cooling thesurface of the resin member 4 on the opposite side from the joiningsurface 5 to a temperature that is lower than the melting point of theresin member 4.

In a case where the joining of the resin member 4 and metal member 3 isperformed by heating the resin member 4 to the melting point ta, the twoare joined only because the joining surface 5 of the resin member 4 thathas reached the melting temperature and softened is deformed along thepeaks and valleys of the joining surface of the metal member 3 and theanchor effect is demonstrated. By contrast, where the joining surface 5of the resin member 4 is heated, as described hereinabove, to atemperature equal to or higher than the decomposition temperature of theresin member 4, the resin member 4 at the joining surface 5 isdecomposed and fusion active groups are created at the joining surface5. The fusion active groups that are created at the joining surface 5 ofthe resin member 4 are bonded by intermolecular forces to the joiningsurface of the metal member 3 with the resin member 4, and joining bythe intermolecular forces of the fusion active groups is conducted inaddition to the joining by the anchor effect on the joining interface ofthe resin member 4 and metal member 3, whereby a high joining strengthcan be obtained.

The joining is thus conducted with a joining apparatus including aheating body 1 that heats the joining interface of the resin member 4and metal member 3 from a surface of the metal member 3 on the oppositeside from the joining surface thereof with the resin member 4, and acooling body 2 that cools the surface of the resin member 4 on theopposite side from the joining surface 5 thereof with the metal member 3to a temperature that is lower than a melting point of the resin member4.

In other words, because the resin member 4 and metal member 3 are joinedby heating the joining surface 5 of the resin member 4 to a temperaturein a range of equal to or higher than a decomposition temperature of theresin member 4 and lower than a temperature at which gas bubbles aregenerated in the resin member 4, neither an adhesive nor a surfacetreatment agent such as an acid, an alkali, and a primer treatment agentis used, a necessary and sufficient joining strength can be obtainedwithin a short time, and environmental load in the process of joiningthe resin member 4 and metal member 3 can be reduced. Further, becausethe heating temperature of the joining surface 5 of the resin member 4is less than a temperature at which gas bubbles are generated in theresin member 4, no gas bubbles are generated at the joining surface 5 ofthe resin member 4 by heating, the occurrence of cracks that originatefrom gas bubbles at the joining interface of the resin member 4 andmetal member 3 can be prevented, and the joining strength of the resinmember 4 and metal member 3 can be ensured after the resin member 4 andmetal member 3 have been joined.

In addition, when the resin member 4 and metal member 3 are joined, thesurface of the resin member 4 on the opposite side from the joiningsurface 5 is cooled to a temperature that is lower than the meltingpoint of the resin member 4. Therefore, this surface is not deformed byheating. Because the resin member 4 can be prevented from thermaldeformation during joining of the resin member 4 and metal member 3, thedesign property of the external surface of the joint body of the resinmember 4 and metal member 3 on the side of the resin member 4 is notreduced and the product value of the joint body can be increased.

For example, various ferrous metals, stainless steel, aluminum materials(including aluminum alloys), magnesium materials (including magnesiumalloys), and copper materials (including copper alloys) can be used asthe material constituting the metal member 3, but this list is notlimiting and other metal materials may be also used.

For example, nylon resins, polyester resins, acrylonitrile butadienestyrene (ABS) resins, and other thermoplastic resins of general use,engineering plastics of general use, super-engineering plastics, andthermoplastic elastomers can be used as the material constituting theresin member 4. A filler such as carbon fibers, glass fibers, talc,mica, kaolin, and calcium carbonate that increases the mechanicalstrength and the like may be admixed to the resin member 4.

In a case where the resin member 4 is constituted by a nonpolar resinthat has absolutely no functional groups, the joining of the resinmember 4 and metal member 3 may be conducted after subjecting thejoining surface 5 of the resin member 4 to a typical dry surfacetreatment such as plasma treatment or corona treatment, without using asurface treatment agent such as an acid, an alkali, or a primertreatment agent. By so joining the resin member 4 and metal member 3after performing the dry surface treatment, it is possible to introducefusion active groups to the joining surface 5 by the surface treatmentmethod with a low environmental load and increase the joining strength.

Further, in a case where the resin member 4 is constituted by a nonpolarresin that has absolutely no functional groups, the joining of the resinmember 4 and metal member 3 is preferably conducted after roughening thejoining surface of the metal member 3 with the resin member 4 by using apolishing tool such as sandpaper or forming peaks and valleys on thejoining surface of the metal member 3 with the resin member 4 byelectron beam processing or laser processing. Where the joining surfaceof the metal member 3 with the resin member 4 is thus provided withroughness or peaks and valleys, the heated resin member 4 can penetrateinto the joining surface of the metal member 3 and demonstrate theanchor effect.

Further, the heating body 1 can be constituted by a high-temperaturesubstance (solid, liquid, or gaseous) that can heat the joining surface5 of the resin member 4 to a temperature in a range of equal to orhigher than a decomposition temperature of the resin member 4 and lowerthan a temperature at which gas bubbles are generated in the resinmember 4 and can be configured so that the heating of the joiningsurface 5 be performed by bringing the high-temperature substance intocontact with the surface of the metal member 3 on the opposite side fromthe joining surface thereof with the resin member 4. Further, theheating body 1 can be constituted to heat the joining surface 5, forexample, by electric resistance heating, high frequency, infraredradiation, or laser radiation, or to heat the joining surface 5 by usingfriction heat created by vibrations or ultrasound. These examples arenot limiting and other heating means may be also used.

The cooling body 2 can be constituted by a low-temperature substance(solid, liquid, or gaseous) that can cool the surface of the resinmember 4 on the opposite side from the joining surface 5 thereof to atemperature that is less than the melting point of the resin member 4,but such a configuration is not limiting and other cooling bodies may bealso used.

An embodiment will be explained below in which, as shown in FIG. 3, themetal member 3 and resin member 4 are joined by using rod-shaped membersas the heating body 1 and cooling body 2, bringing the rod-shapedheating body 1 into contact with the surface of the metal member 3 onthe opposite side from the joining surface thereof with the resin member4 to conduct heating and similarly bringing the rod-shaped cooling body2 into contact with the surface of the resin member 4 on the oppositeside from the joining surface 5 to conduct cooling.

The heating body 1 and cooling body 2 of the present embodiment areformed to a shape similar to that of a gun of a spot welding machine.More specifically, the heating body 1 and cooling body 2 aresubstantially cylindrical columnar members in which the end portionsthereof on the side that will come into contact with the metal member 3and resin member 4, respectively, are tapered, and these cylindricalcolumnar members are disposed on both sides of the metal member 3 andresin member 4 in a state in which the metal member 3 and resin member 4are stacked. The heating body 1 is pressed against the metal member 3,the cooling body 2 is pressed against the resin member 4, and the metalmember 3 and resin member 4 are pressed together in a state in which themetal member 3 and resin member 4 are stacked. As a result, the joiningsurface 5 of the resin member 4 is melted by heat from the heating body1 and also decomposed, thereby joining the resin member 4 to the metalmember 3. In this case, the surface of the resin member 4 that has comeinto contact with the cooling body 2 is cooled by the cooling body 2and, therefore, prevented from thermal deformation. Because the heatingbody 1 and cooling body 2 are formed to a shape similar to that of a gunof a spot welding machine, a line and system of the spot welding machinecan be used in the process of joining the metal member 3 and resinmember 4.

Further, as shown in FIG. 4, the heating body 1 and cooling body 2 maybe constituted by roller members. The heating body 1 and cooling body 2constituted by roller member are disposed opposite each other at adistance equal to or slightly less than the thickness of the metalmember 3 and resin member 4 in a stacked state thereof.

By feeding the metal member 3 and resin member 4 in a stacked statethereof between the heating body 1 and cooling body 2 disposed oppositeeach other and squeezing the metal member 3 and resin member 4 in astacked state thereof by the heating body 1 and cooling body 2, thejoining surface 5 of the resin member 4 is melted by the heat of theheating body 1 and decomposed, whereby the metal member 3 and resinmember 4 are joined together. In this case, the surface of the resinmember 4 that comes into contact with the cooling body 2 is cooled bythe cooling body 2 and, therefore, prevented from thermal deformation.When the joining of the metal member 3 and resin member 4 is performed,the metal member 3 and resin member 4 that have been fed between theroll-shaped heating body 1 and cooling body 2 are successively conveyedby rotation of the heating body 1 and cooling body 2, thereby making itpossible to join the metal member 3 and resin member 4 continuously, asin seam welding.

The metal member 3 may have the following configuration. Thus, as shownin FIGS. 5 to 7, slits (cavities) 3 a can be formed in the metal member3 on the circumference of a joining region 6 of the metal member 3 andresin member 4. The slits 3 a pass through the metal member 3 in thejoining direction thereof to the resin member 4 and are formed in aplurality of places on the circumference of the joining region 6.

As shown in FIG. 6, portions where the slits 3 a are formed in the metalmember 3 are cavities. Therefore, heat transfer between two sides of themetal member 3 that sandwich the slits 3 a (between a zone on the innerside of the slits 3 a and zone outside the slits) is prevented.Therefore, heat supplied from the heating body 1 through the metalmember 3 to the joining interface of the metal member 3 and resin member4 can be prevented from diffusing to the outside in the plane directionof the joining region 6 and the joining region 6 can be efficientlyheated. Further, because heat is not transferred to the outside of theslits 3 a, the joining of the metal member 3 and resin member 4 is notconducted, thereby enabling the joining region 6 to be controlled withgood accuracy.

At the joining surface 5 of the resin member 4, because the resin member4 melts within a region somewhat wider than the joining region 6, themolten and softened resin member 4 penetrates into the slits 3 a, asshown in FIG. 8. Thus, an anchor effect is produced in the portion wherethe resin member 4 has penetrated into the slits 3 a of the metal member3 and, therefore, the joining strength of the metal member 3 and resinmember 4 after joining can be increased.

Thus, by forming the slits 3 a on the circumference of the joiningregion 6 in the metal member 3, it is possible to inhibit heat transferbetween the portions of the metal member 3 on both sides of the slits 3a, and the heat that is supplied to the joining interface of the metalmember 3 and resin member 4 from the heating body 1 via the metal member3 is prevented from diffusing to the outside in the plane direction ofthe joining region 6 (see FIG. 6).

As shown in FIG. 7, the slits 3 a are formed so as to cover the entireregion on the circumference of the joining region 6, but the ratio atwhich the circumference of the joining region 6 is covered may bechanged appropriately. Thus, the region covered by the slits 3 a can beappropriately determined correspondingly to the degree to which thediffusion of heat transferred to the joining region 6 in the planedirection is inhibited. Further, the slits 3 a that are formed in themetal member 3 may be formed by cutting with a cutting tool ormachining, e.g., punching, and also by processing with a laser orelectron beam.

Instead of forming the above-described slits 3 a in the metal member 3,it is also possible to form grooves 3 b, as shown in FIGS. 9 and 10, asa structure that prevents heat transfer to the outside of the joiningregion 6. The grooves 3 b are formed from the surface of the metalmember 3 on the opposite side from the joining surface thereof with theresin member 4 toward the joining interface side. In other words, thegrooves 3 b are opened at the surface of the metal member 3 on theopposite side from the joining surface thereof with the resin member 4and are closed and have a bottom portion on the joining interface sideof the metal member 3 with the resin member 4.

Similarly to the slits 3 a, the grooves 3 b are formed in a plurality ofplaces on the circumference of the joining region 6, and heat suppliedfrom the heating body 1 to the joining interface of the metal member 3and resin member 4 through the metal member 3 can be prevented fromdiffusing to the outside in the plane direction of the joining region 6.In a case where the grooves 3 b are formed as a configuration thatinhibits the diffusion of heat transferred to the joining region 6 tothe outside in the plane direction, a bottom portion is formed in thegrooves 3 b at the joining interface side of the metal member 3 andresin member 4 and the grooves 3 b do not pass as the aforementionedslits 3 a through the metal member 3. Therefore, the rigidity of themetal member 3 can be increased by comparison with that in the case inwhich the slits 3 a are formed in the metal member 3.

Grooves 3 c and grooves 3 d can be also formed respectively on thejoining interface side of the metal member 3 with the resin member 4 andon the surface side on the opposite side from the joining interfaceside, as shown in FIG. 11, as a structure that prevents heat transfer tothe outside of the joining region 6. The grooves 3 c are opened at thejoining surface of the metal member 3 with the resin member 4 and have abottom in the intermediate portion in the thickness direction of themetal member 3. The grooves 3 d are opened at the surface on theopposite side from the joining interface and have a bottom in theintermediate portion in the thickness direction of the metal member 3.The grooves 3 c and grooves 3 d are disposed in substantially identicalpositions in the plane direction of the metal member 3, and the grooves3 c share bottom portions with the grooves 3 d.

Further, similarly to the slits 3 a, the grooves 3 c and 3 d are formedin a plurality of places on the circumference of the joining region 6,and heat supplied from the heating body 1 to the joining interface ofthe metal member 3 and resin member 4 through the metal member 3 can beprevented from diffusing to the outside in the plane direction of thejoining region 6. Thus, in a case where the grooves 3 c and 3 d areformed as a configuration that inhibits the diffusion of heattransferred to the joining region 6 to the outside in the planedirection, a bottom portion of each pair of grooves 3 c and 3 d isformed between the grooves 3 c and grooves 3 d of the metal member 3,and the grooves 3 c and 3 d do not pass as the aforementioned slits 3 athrough the metal member 3. Therefore, the rigidity of the metal member3 can be increased by comparison with that in the case in which theslits 3 a are formed in the metal member 3. Further, the melted andsoftened resin member 4 penetrates into the grooves 3 c, therebygenerating the anchor effect in the portions where the resin member 4has penetrated into the grooves 3 c of the metal member 3.

Grooves 3 e such as shown in FIGS. 12 and 13 can be also formed as astructure that prevents heat transfer to the outside of the joiningregion 6. The grooves 3 e are formed from the joining surface of themetal member 3 with the resin member 4 toward the surface on theopposite side from the joining surface. In other words, the grooves 3 eare opened at the joining surface of the metal member 3 with the resinmember 4 and are closed and have a bottom at the surface of the metalmember 3 on the opposite side from the joining surface of the metalmember 3 with the resin member 4.

Similarly to the slits 3 a, the grooves 3 e are formed in a plurality ofplaces on the circumference of the joining region 6, and heat suppliedto the joining interface of the metal member 3 and resin member 4 can beprevented from diffusing to the outside in the plane direction of thejoining region 6. In a case where the grooves 3 e are formed as aconfiguration that inhibits the diffusion of heat transferred to thejoining region 6 to the outside in the plane direction, a bottom portionof the groove 3 e is formed at the surface of the metal member 3 on theopposite side from the joining surface thereof with the resin member 4and the grooves 3 e do not pass, as the aforementioned slits 3 a,through the metal member 3. Therefore, the rigidity of the metal member3 can be increased by comparison with that in the case in which theslits 3 a are formed in the metal member 3.

In the configuration in which the grooves 3 b shown in FIGS. 9 and 10are formed in the metal member 3, the heating body 1 shown in FIG. 3etc. may be disposed at the surface side opposite from the joiningsurface side of the metal member 3 with the resin member 4, and thejoining interface of the metal member 3 and resin member 4 may be heatedfrom the side of the metal member 3. Further, in the configuration inwhich the grooves 3 e shown in FIGS. 12 and 13 are formed in the metalmember 3, the joining interface of the metal member 3 and resin member 4may be heated from the side of the resin member 4 by using thebelow-described high-frequency heating apparatus 11 or laser irradiationapparatus 12. Further, in the configuration in which the slits 3 a shownin FIGS. 5 to 7 and grooves 3 c and 3 d shown in FIG. 11 are formed inthe metal member 3, the heating may be performed from the side of themetal member 3 or from the side of the resin member 4.

Further, as shown in FIG. 14, when the joining interface of the metalmember 3 with the resin member 4 is heated, the high-frequency heatingapparatus 11 may be used as the heating tool. When the joining interfaceis heated by using the high-frequency heating apparatus 11, a thin film8 is inserted between the metal member 3 and resin member 4, and thehigh-frequency heating apparatus 11 is disposed on the surface side ofthe resin member 4 on the opposite side from the joining surface 5.

The heating method in which the thin film 8 is inserted between themetal member 3 and resin member 4 and the joining interface of the metalmember 3 and resin member 4 is heated using the high-frequency heatingapparatus 11 can be applied when the metal member 3 is a non-magneticmaterial having a low thermal conductivity and a low electricresistance, such as aluminum (Al) and copper (Cu).

In this case, a magnetic material with an electric resistance higherthan that of the metal member 3, for example, a metal material such asiron (Fe), nickel (Ni), and cobalt (Co) may be used as the thin film 8.The thin film 8 may be provided by subjecting the joining surface of themetal member 3 with the resin member 4 to various processing methods,for example, electroplating, spraying, or cold spraying with theaforementioned metal materials. The metal member 3 and resin member 4are joined together by stacking the metal member 3 provided with thethin film 8 with the resin member 4 and then high-frequency heating thethin film 8 interposed in the joining interface of the metal member 3with the resin member 4 using the high-frequency heating apparatus 11.

Generally, in a case where the metal member 3 is constituted by amaterial with a high thermal conductivity and a low electric resistance,such as aluminum (Al) and copper (Cu), when the metal member 3 is heatedfrom the surface on the side opposite from the joining surface thereofwith the resin member 4 and the joining interface is heated by the heattransferred to the metal member 3, the heat transferred to the metalmember 3 from the surface on the opposite side from the joining surfacediffuses over a large range, the efficiency of heat input to the joiningregion 6 of the metal member 3 and resin member 4 is low, and the heatinput range is difficult to control.

By contrast, when the thin film 8 is interposed in the joining interfaceof the metal member 3 and resin member 4 and the thin film 8 is directlyheated by the high-frequency heating apparatus 11 disposed on the sideof the resin member 4, the joining surface 5 of the resin member 4 isheated to a temperature in a range of equal to or higher than adecomposition temperature of the resin member 4 and lower than atemperature at which gas bubbles are generated in the resin member 4.

Where the thin film 8 disposed at the joining interface of the metalmember 3 and resin member 4 is thus directly heated, the efficiency ofheat input in the joining region 6 can be increased even when the metalmember 3 is constituted by a material with a high thermal conductivityand a low electric resistance. Further, by constituting the heating body1 by the high-frequency heating apparatus 11 and forming the heatingcoil of the high-frequency heating apparatus 11 to a size correspondingto the size of the joining region 6, it is possible to control the rangeof heat input to the joining interface of the metal member 3 and resinmember 4. As a result, joining can be performed by adequately heatingthe joining interface of the metal member 3 and resin member 4 within ashort period by a simple process and a sufficient joining strength canbe obtained. In the above-described configuration, only thehigh-frequency heating apparatus 11 is used as the heating tool thatheats the joining interface of the metal member 3 and resin member 4,but the high-frequency heating apparatus 11 may be used together withthe heating body 1 and/or cooling body 2.

Further, as shown in FIG. 15, in a case where the joining interface ofthe metal member 3 and resin member 4 is heated, the laser irradiationapparatus 12 can be used as the heating body 1 and heating can beperformed by irradiating the joining interface with the laser radiationfrom the laser irradiation apparatus 12. In a case where heating isperformed by irradiating the joining interface with the laser radiationfrom the laser irradiation apparatus 12, a thin film 9 is interposedbetween the metal member 3 and resin member 4 and the laser irradiationapparatus 12 is disposed at the surface on the side opposite from theside of the joining surface 5 of the resin member 4.

The heating method in which the thin film 9 is inserted between themetal member 3 and resin member 4 and the joining interface of the metalmember 3 and resin member 4 is heated using laser radiation from thelaser irradiation apparatus 12 can be applied when the metal member 3 isa material having a low thermal conductivity and a high reflectance oflaser radiation in the infrared region, such as aluminum (Al) and copper(Cu).

In this case, the resin member 4 may be constituted by a material thatcan transmit the laser radiation, and a metal material with reflectanceof laser radiation in the infrared region lower than that of the metalmember 3, for example, iron (Fe), nickel (Ni), cobalt (Co), and zinc(Zn) may be used as the thin film 9. The thin film 9 may be provided bysubjecting the joining surface of the metal member 3 with the resinmember 4 to various processing methods, for example, electroplating,spraying, or cold spraying with the aforementioned metal materials.

The metal member 3 and resin member 4 are joined together by stackingthe metal member 3 provided with the thin film 9 with the resin member 4and then heating the joining interface by irradiating the thin film 9interposed in the joining interface of the metal member 3 with the resinmember 4 with laser radiation, from the laser irradiation apparatus 12.The laser irradiation apparatus 12 may be constituted by an apparatusthat emits infrared laser radiation, such as a yttrium aluminum garnet(YAG) laser, a semiconductor laser, or a CO₂ laser.

Generally, in a case where the metal member 3 is constituted by amaterial with a high reflectance of infrared laser radiation, such asaluminum (Al) and copper (Cu), even when the joining surface of themetal member 3 with the resin member 4 is irradiated with laserradiation, most of the radiation is reflected at the joining surface. Asa result, the heating efficiency is poor and the metal member 3 andresin member 4 are difficult to join together by heating by irradiationwith laser radiation.

By contrast, where the thin film 9 is interposed in the joininginterface of the metal member 3 and resin member 4 and laser radiationis emitted toward the thin film 9 from the laser irradiation apparatus12 disposed on the side of the resin member 4, the joining surface 5 ofthe resin member 4 is heated to a temperature in a range of equal to orhigher than a decomposition temperature of the resin member 4 and lowerthan a temperature at which gas bubbles are generated in the resinmember 4.

Where the thin film 9 disposed at the joining interface of the metalmember 3 and resin member 4 is thus heated by laser radiation, theefficiency of heat input in the joining region 6 can be increased evenwhen the metal member 3 is constituted by a material with a highreflectance of laser radiation and joining of the metal member 3 andresin member 4 can be easily realized by heating by irradiation withlaser radiation. Further, by constituting the heating body 1 by thelaser irradiation apparatus 12 and forming the irradiation range oflaser radiation from the laser irradiation apparatus 12 to a sizecorresponding to the size of the joining region, 6, it is possible tocontrol the range of heat input to the joining interface of the metalmember 3 and resin member 4. As a result, joining can be performed byadequately heating the joining interface of the metal member 3 and resinmember 4 within a short period by a simple process and a sufficientjoining strength can be obtained. In the above-described presentexample, only the laser irradiation apparatus 12 is used as the heatingtool that heats the joining interface of the metal member 3 and resinmember 4, but the laser irradiation apparatus 12 may be used togetherwith the heating body 1 and/or cooling body 2.

The invention claimed is:
 1. A joining method for joining a resin and ametal by heating, the method comprising: joining the resin and the metalby heating a joining interface of the resin and the metal to atemperature in a range of equal to or higher than a decompositiontemperature of the resin and lower than a temperature at which gasbubbles are generated in the resin, wherein a concavity is formed in azone of the metal around a joining region of the resin and the metal,wherein the concavity is formed prior to heating the joining interface,and wherein the concavity is formed so as to prevent heat transfer fromdiffusing to an outside in a plane direction of the joining region. 2.The joining method according to claim 1, wherein: the joining interfaceof the resin and the metal is heated from a surface of the metal on theopposite side from a joining surface thereof with the resin; and asurface of the resin on the opposite side from a joining surface thereofwith the metal is cooled to a temperature that is lower than a meltingpoint of the resin.
 3. The joining method according to claim 1, whereinthe joining of the resin and the metal is performed by interposing athin film having an electric resistance higher than that of the metal inthe joining interface of the resin and the metal and high-frequencyheating the thin film from a surface of the resin on the opposite sidefrom a joining surface thereof with the metal.
 4. The joining methodaccording to claim 1, wherein: a thin film having a laser reflectancelower than that of the metal is interposed in the joining interface ofthe resin and the metal; the resin is constituted by a material thattransmits laser radiation; and the joining of the resin and the metal isperformed by emitting laser radiation toward the thin film from asurface of the resin on the opposite side from a joining surface thereofwith the metal and heating the thin film.